The present invention relates to the estimation of the height of the center of gravity of a vehicle, and in particular of an industrial vehicle.
The height of the center of gravity (COG) of a vehicle has a strong impact on its behavior on road. Various systems tend to automatically control the behavior of the vehicle using the height of COG as a key parameter. This is the case for ESP functions and also for other dynamic control assistance. Thus, the height of COG should be determined with enough precision to avoid inappropriate activation of these dynamic control systems. The mass of a vehicle is commonly used to evaluate the height of its COG. However, depending of the nature of the payload, the mass may not be relevant enough. Furthermore, from one mission to the other, the nature of the payload may change, rendering the determination of the height of COG even more difficult. Thus, there is a need to improve the determination of the height of COG under true driving conditions.
WO2011036511 provides a method to evaluate the height of COG of a commercial vehicle having 2 axles. It is desirable to determine the height of COG for vehicles having more than 2 axles. Other prior art refers to methods for estimating the height of COG for a vehicle such as patent application US2011224895, especially vehicles comprising a trailer coupled to a tractor such as international patent applications WO2013141787 and WO2004074804 and the publication of Deleer Barazanji concerning “Model Based Estimation of Height of Centre of Gravity in Heavy Vehicles”.
It is desirable to determine the height of COG of a vehicle in motion, and more particularly when the speed of the vehicle varies. This method, according to an aspect thereof, applies more specifically to vehicles having more than two axles, e.g. vehicles having 3, 4, 5 or more axles. This method is, according to an aspect thereof, therefore well appropriate to industrial vehicles in general.
It is also desirable to consider the parameters already sensed within the vehicle, in such a way that there is no need to add specific sensors or devices.
3 reference points are predetermined within the vehicle. A reference point, in the sense of the present invention, means a physical point or a virtual point within the vehicle, wherein tangential and normal forces are determined. The values of these tangential and normal forces are then computed to determine the height of the COG. In particular, in case of a rigid vehicle having 3 axles, the 3 reference points coincide with the 3 axles of the vehicle. In case the vehicle is a combination of a tractor and a semi-trailer, a reference point corresponds to the first axle of the tractor, another reference point corresponds to an axle of the semi-trailer, and the last reference point corresponds to the fifth wheel of the tractor.
Above and below, the tangential forces include the forces tangential to the wheels at the point of contact with the ground. They are applied to the running direction of the vehicle, during an acceleration, and opposite to the running direction of the vehicle during a braking phase. A tangential force may be applied similarly at any other point within the vehicle, like the fifth wheel of a tractor. For the purpose of the present method, the tangential forces preferably denote forces opposite to the running direction of the vehicle. Tangential forces can thus result from the braking forces of the braking system of the vehicle, the retarder or any other forces that slow down the vehicle, as well as the combination thereof.
The normal forces are orthogonal to the tangential forces and mainly result from the weight of the vehicle. The normal forces vary in case of change of speed of the vehicle, and in particular during the braking phases.
Above and below, a driving force should be understood as the force provided by the engine, or the electrical system in case of an hybrid or electrical vehicle, and includes the resistive forces such as the retarder, and the engine brake. The driving force has a tangential resultant and a normal resultant.
Above and below, a rigid truck means a vehicle which is not articulated. It can be a carrier, a tractor of a semi-trailer, without the semi-trailer, or any other non-articulated vehicle. It comprises one or more steering axles, preferably one steering axle and one or more driving axles.
The present method, according to an aspect thereof, comprises a first step of determining the tangential forces at all the axles of the vehicle. In case of a combination of a tractor and a semi-trailer, the tangential forces at the axles of the tractor and semi-trailer are considered.
The present method, according to an aspect thereof, comprises a second step of deducing the corresponding normal forces from the tangential forces, previously determined. The normal force at a given axle is deduced from the corresponding tangential force thanks to the slippage rate of the wheels of said axle. For easiness, it may be considered that all the wheels of a given axle have the same slippage rate. However, the method may be applied with various slippage rates from one wheel to the other. For the purpose of the present method, the slippage rate should be maintained as low as possible. In particular, the method may be considered reliable as long as the slippage rate is equal or below about 10% at each wheel.
It is envisaged than when one of the reference points does not correspond to an axle of the vehicle, then a separate step may be initiated to determine the normal force at said reference point. This may be the case for example when the vehicle is a combination of a tractor and a semi-trailer, wherein the fifth wheel is a reference point. In that case, the normal force at the fifth wheel is determined on the basis of the tangential and normal forces determined at the axles of the tractor. It has to be noted that in this particular case, the determination of the normal force at the fifth wheel only considers the tangential and normal forces determined at the wheels of the tractor.
The steps above-discussed, performed during an acceleration phase, lead to the determination of the normal forces at each of the 3 reference points of the vehicle. An acceleration phase includes any period wherein the speed of the vehicle increases, as well as any period wherein the speed of the vehicle decreases. For the purpose of the present method, the braking period, wherein the speed decreases, will preferably be considered. However similar reasoning can be established using the driving torque applied to the axles during an acceleration phase, instead of considering the braking forces during a braking phase. During the braking periods, the braking pressure actually applied to the wheels is easily known, thanks to sensors present in the braking system. Thus, the tangential forces are easily determined.
An acceleration phase or an acceleration period should be understood as any period of time where the speed of the vehicle changes. The speed may increase or decrease. The present method can apply to acceleration phases where the speed of the vehicle varies in a non-homogenous way. However, an acceleration phase or acceleration period preferably denotes a period of time where the speed of the vehicle varies homogeneously. In other words, it preferably corresponds to a period of time where the acceleration remains constant. An acceleration phase or acceleration period lasts from few milliseconds to several seconds.
The steps above discussed are therefore performed together within a single acceleration phase. These steps are reiterated during at least one additional acceleration phase. The acceleration of the vehicle during this additional acceleration phase is preferably different from the acceleration of the vehicle during the first acceleration phase. Preferably, the acceleration of the vehicle between a first and a second acceleration phase differs by more than 10%, more preferably by more than 20% and most preferably by more than 50%. The values of the normal forces at the 3 references points, determined during the first acceleration phase, are computed with the corresponding values determined during the second acceleration phase according to an algorithm, in such a way that the height of the COG can be evaluated.
Although 2 sets of values, determined during 2 distinct acceleration phases, may be enough to determine the height of COG, the steps above-discussed can be repeated several times. All the values corresponding to the height of COG can further be computed to provide an average value.
It has to be noted that a first and a second acceleration phase, during which are generated the 2 sets of values above discussed, may be both part of the same acceleration operation, or may be part of distinct acceleration operations.
Thus, the present method, according to an aspect thereof, comprises the following steps:
Determining the tangential forces at all the axles of the vehicle, during a first acceleration phase,
Deducing from the tangential forces determined in step a) the corresponding normal forces during the first acceleration phase,
Optionally determining the normal force at one of the predetermined reference points, if not already determined through steps a) and b), during a first acceleration phase, using the values determined in steps a) and b).
Repeating steps a), b), and c) at least once during a second acceleration phase distinct from the first acceleration phase,
Deducing from the preceding steps a), b), c) and d) the height of the gravity center G of the vehicle, or an element of said vehicle, by computing the normal forces at said 3 predetermined reference points, using an algorithm.
The present method, according to an aspect thereof, further comprises the optional step:
Repeating steps a) to e) several times and providing an average value of the height of COG.
For the specific case of a rigid vehicle comprising 3 axles, each corresponding to a reference point, the present method may be written as follows:
Determining the tangential forces at the 3 reference points corresponding to the 3 axles of the vehicle, during a first acceleration phase,
Deducing from the tangential forces determined in step a) the corresponding normal forces during the first acceleration phase,
d) Repeating steps a) and b) at least once during a second acceleration phase, wherein the acceleration of the vehicle is distinct from the first acceleration, and
e) Deducing from the preceding steps the height of the gravity center G of the vehicle, by using one or more algorithms.
f) Optionally repeating steps a), b), d) and e) several times, and providing an average value of the height of COG.
For the specific case of a combination of a tractor and a semi-trailer, the method may be written as follows:
Determining the tangential forces at all the axles of the tractor and the semi-trailer, during a first acceleration phase,
Deducing from the tangential forces determined in step a) the corresponding normal forces during the first acceleration phase,
Determining the normal force at the fifth wheel of the tractor, during a first acceleration phase, using the values of the tangential and normal forces at the axles of the tractor only, determined during the steps a) and b),
Repeating steps a), b), and c) at least once during a second acceleration phase, wherein the acceleration of the vehicle is distinct from the first acceleration, and
Deducing from the preceding steps the height of the gravity center G of the semi-trailer, by computing the normal forces at the first axle of the tractor, a rear axle of the semi-trailer and at the fifth wheel, according to an algorithm.
The following optional step is still valid:
Repeating steps a) to e) several times and providing an average value of the height of COG.
The present invention also encompasses, according to an aspect thereof, a vehicle wherein the determination of the height of the gravity center is determined according to the method hereby described.